Due to the excellent injection molding and machine physical properties, polyester resin and polyamide resin are applied in a wide range of fields such as mechanical and machinery components, electrical and electronic components, and automobile components. At the same time, polyester resin and polyamide resin are crystalline plastics, in particular, the glass fiber reinforced polyester resin and polyamide resin, so they are used for the extruder and injection molding machine needing the high processing temperature for melting mixing.
However, as polyester resin and polyamide resin are combustible in nature, in addition to the balance between the chemical and physical characteristics, the safety of the flame, i.e. the fire resistance is also required when they are used as the industrial materials such as the mechanical and machinery components, electrical and electronic components, and automobile components. In most cases, it is necessary to display V-0 high fire resistance under the UL-94 standard. The method giving the fire resistance to polyester resin and polyamide resin generally mixes up the halogen organic composition as the fire retardant and the antimony composition as the flame retardant agent into the resin. However, as the result of the improvement in the environmental awareness, people begin to worry about the impact of the halogen organic composition to the environment. Therefore, it has been proposed in recent years to use the fire retardant without any halogens as well as the thermoplastic resin mixed with phosphorus composition as the fire retardant.
The salt of phosphinic acid (hypophosphite) has been proven to be an effective flame retardant additive for the thermoplastic polymer, and is also applicable to the alkali metal salt and other metal salts (See DE 225225A and DE 2477727A). Calcium hypophosphite and aluminum hypophosphite have been described as particularly effective in the polyester and cause less damage to the material performance in the polymer molding plastic composition compared to the corresponding alkali metal salt. See EP 0699708A.
Some literature also disclose the synergistic interaction combination of the phosphinic acid salt and nitrogen-containing composition, which shall be a more effective fire retardant in a large amount of the polymers compared to a single hypophosphite. See PCT/EP97/01664, DE 19734437A, and DE 19737727A.
When the phosphinic acid salt exists in the fire-resistant polyester or polyamide composition as a separate component or together with other flame retardants, it usually leads to the polymer degradation to certain extent due to the higher acidity of hypophosphite, which possibly has the adverse effect on the mechanical performance and even the electrical performance. The corrosive gas produced by the flame retardant corrodes the screw of the mixing unit or the die of the injection molding. Furthermore, the corrosive gas corrodes the metals of the terminals, which contact the flame-retardant thermoplastic resin molded product, resulting in the pollution to the contact. Therefore, it is urgent to solve the problem in the corrosion of the fire-retardant resin to the metal.
At present, some published literatures elaborate several solutions to the problem, for example, see CN 201080006709.2. It is possible to improve the corrosiveness by adding a compound as follows:
However, the compound has limited heat resistance, so it is difficult to apply for the system with the higher requirement for the processing temperature (e.g., the fiber reinforced system). CN 200880130162.X solves the problem in corrosion by adding the zinc stannate, however, the addition of zinc stannate causes degradation of the mechanical performance, in particular the impact resistance of the product. Therefore, it is urgent to solve the problem in the corrosion of the hypophosphite as an additive in the process of high-temperature molding processing.